The present invention relates to a synthetic equivalent test circuit to verify a large current breaking performance of a power circuit breaker and, more particularly, to a circuit to generate a 4-parameter transient recovery voltage (hereinafter, abbreviated to TRV).
The progress of development of the large capacity power circuit breaker has been remarkable. In recent years, a circuit breaker having rated voltages from 362 to 420 kV has been constructed with one break per phase. Further, a study is carried out to realize the circuit breaker having a rated voltage 550 kV with single-break.
On the other hand, according to the International Electrotechnical Commission (hereinafter, abbreviated to IEC) and the Japanese Electrotechnical Committee (hereinafter, abbreviated to JEC) regarding the breaking tests of a large capacity power circuit breaker, what is called a 4-parameter TRV in which a peak value appears later is specified as a voltage waveform which is applied between poles of a circuit breaker which interrupted the current.
That is, the 4-parameter TRV means that after the current of a predetermined magnitude was broken, there are specified four parameters comprising first and second reference times of voltage waveform which are applied between the contacts of the circuit breaker to be tested and first and second reference voltage values at those times, and if the four parameters satisfy request values, it is determined that the testing circuit breaker has a desired breaking performance.
However, the TRV which is generated by a Weil synthetic equivalent test circuit which has conventionally widely been used for verification of the breaking performance relates to the oscillation of a single frequency and is called a 2-parameter TRV. Therefore, many methods of improving the test circuit so that they can generate a 4-parameter TRV have been proposed. However, there are economical and technical subjects. Only a few examples of such improved test circuits have been put into practical use for the commercially available tests and are not widely used yet.
The 2-parameter TRV denotes that for the above 4-parameter TRV, two parameters of only one reference time t.sub.3 of a voltage waveform which is applied between the contacts of a testing circuit breaker after the current was broken and a reference voltage value u.sub.c at that time are specified and if the two parameters satisfy the specified values, it is decided that the testing circuit breaker has an enough breaking performance.
As mentioned above, there is a problem such that as the number of breaks per pole of the circuit breaker decreases, it is severer for the 2-parameter TRV than a specified TRV or the like. The necessity of a circuit which can economically generate a 4-parameter TRV having a long peak time t.sub.2 for a 2-parameter TRV having a short peak time is more and more increasing.
FIG. 1 shows an embodiment of a conventional 4-parameter TRV generating circuit. FIG. 2 is a diagram for explaining a phenomenon in the circuit of FIG. 1.
The above conventional 4-parameter TRV generating circuit has been disclosed in the literature by ISAO TAKAHASHI, MINORI SATOH, and SHUNJI TOKUYAMA (all of them belong to Hitachi Research Laboratory, HITACHI, LTD., Japan), "FOUR-PARAMETER TRANSIENT RECOVERY VOLTAGE CIRCUITS APPROPRIATE FOR TESTING OF EXTRA HIGH VOLTAGE CIRCUIT BREAKERS", IEEE Transactions on Power Delivery, Vol. 3, No. 1, page 233, FIGS. 3 and 4, January, 1988.
In FIG. 1, the left side diagram including a circuit breaker 1 which is used for testing shows a current source circuit of a low voltage and the remaining right side shows a voltage source circuit of a high voltage. A current source current i.sub.c is supplied to an auxiliary switch 9 arranged in the voltage source circuit from on A.C. power source 2 through a reactor 3 for current adjustment, a transformer 18, and an auxiliary circuit breaker 4. The current i.sub.c flows through the auxiliary switch 9 and the testing circuit breaker 1. In this case, a current source protection surge absorber 5 is connected to the position shown in the diagram in many cases.
After the current was allowed to flow, the auxiliary circuit breaker 4 to protect the circuit from a high voltage and auxiliary switch 9 and the circuit breaker 1 to be tested are closed and the current source current i.sub.c is supplied. After that, for instance, the auxiliary circuit breaker 4, auxiliary switch 9, and testing circuit breaker 1 are almost simultaneously opened. A control gap 7 is discharged just before the final zero point of the current source current i.sub.c. A voltage source current i.sub.v is allowed to flow from a capacitor 6, which has previously been charged, through the control gap 7, a reactor 8, the auxiliary switch 9, and the testing circuit breaker 1 as shown in FIGS. 1 and 2.
An injection time point of the voltage source current i.sub.v is located before the current zero period of the current source current i.sub.c because the current injection method is used here. Also, a period (t.sub.0) of only the voltage source current lies within a range from 1/8 to 1/4 of a period (T) of the voltage source current.
In FIG. 1, when the testing circuit breaker 1 has succeeded in breaking the current, currents i.sub.1 to i.sub.3 flow by a residual voltage in the capacitor 6 as shown in FIG. 2. A branch path in which the current i.sub.1 flows comprises a series circuit of a resistor 10 and a capacitor 11b. A branch path in which the current i.sub.2 flows comprises a series circuit of a resistor 12 and a capacitor 13. On the other hand, as shown in FIG. 1, the current i.sub.3 flows in a series circuit of a reactor 15 and a resistor 16. In result, the current of (i.sub.1 -i.sub.3) flows to a capacitor 11a and the current of (i.sub.2 +i.sub.3) flows to a capacitor 14.
The circuit conditions are designed and constructed in a manner such that electrostatic capacities of the capacitors 11 and 14 are fairly larger than the electrostatic capacity of the capacitor 13 (C.sub.11, C.sub.14 &gt;&gt;C.sub.13) by the method which has been predetermined by the foregoing literature, "IEEE Transactions on Power Delivery, Vol. 3, No. 1, January, 1988". Due to this, when the voltage source current i.sub.v is broken by the testing circuit breaker 1, the current i.sub.2 and a voltage TRV.sub.1 as an initial portion of a target TRV as shown in FIG. 2 are generated as a voltage drop of a serial circuit of the resistor 12, capacitor 13, and capacitor 14.
By properly selecting the circuit conditions, a next current zero point i.sub.20 of the current i.sub.2 can be generated at a time point which is earlier than a next current zero point i.sub.10 of the current i.sub.1. Although the auxiliary switch 9 can be constructed by various forms, the above related art corresponds to a method which can be easily handled and in which an arc between contacts is ignited by supplying the current source current i.sub.c to the auxiliary switch 9, thereby allowing the voltage source current i.sub.v to be easily supplied, and a breaking performance of the current i.sub.2 is given, and there is no need to increase the control gap.
When the current i.sub.2 is broken at the next current zero point i.sub.20 by the above method, if the circuit comprising the reactor 15 and the resistor 16 does not exist in FIG. 1, as shown by an alternate long and short dash line in FIG. 2, a terminal voltage of the testing circuit breaker 1 continuously keeps a predetermined value near an initial peak value u.sub.l of the TRV. In this case, almost of the voltage exists across the capacitor 13 and a terminal voltage of the capacitor 14 is sufficiently low. Therefore, as shown in the diagram, by previously selecting a proper number of stages from among multi-stage serial capacitors 11 and by connecting as the capacitor 11a to the capacitor 14 through the reactor 15 and the resistor 16, the voltage of the capacitor 14 can be raised with a delay time by the current i.sub.3 (such a change assumes TRV.sub.2) and a voltage suitable for a 4-parameter indication shown by (TRV.sub.1 +TRV.sub.2) can be applied to the testing circuit breaker 1.
When such a 4-parameter TRV generating circuit is put into practical use, the auxiliary switch 9 causes the largest problem. The further improvement is demanded from a viewpoint of the evaluation of the breaking performance and from a technical or economical viewpoint.
The above conventional technique intends to accomplish the object by allowing all of the short-circuit current i.sub.c from the power source 2 to supply a current to the auxiliary circuit breaker 4, the testing circuit breaker 1 and the auxiliary switch 9. In the case of the auxiliary switch 9, since a breaking portion is damaged by a large current arc, it is necessary to execute the inspection and maintenance frequently and the improvement is required to manage the equipment. On the other hand, there is also a fear such that the breaking operation of the testing circuit breaker 1 is assisted by the generation of the arc voltage of the auxiliary switch 9 and the evaluation of the performance is made advantageously.